1. Field of the Invention
This invention relates to a packing material comprising a thermosetting resin and a particulate filler, and to a method of making the packing material. More specifically, the present invention relates to a packing material for sealing an electric device such as an integrated circuit (IC), a large scale integrated circuit, transistor, etc., and relates to a method for making the packing material. These electronic devices are mainly manufactured from silicon wafers. After printing an electronic circuit pattern, the silicon wafer is brought into a dicing process wherein the wafer is cut into individual chips. Then the chip is mounted to a base, and terminals are bonded onto the base. The electronic devices can work after bonding, but usually the chip is sealed by a packing material for protection. There are some existing methods and materials for sealing (packaging) the chip. For example, one method involves covering the chip with a metal casing, whereas in another the chip is entirely covered with a material having fluidity under specified conditions, such as glass, ceramics or resin. The present invention particularly relates to a packing material comprising thermosetting resin and filler particles.
2. Description of Related Art
In one of the conventional methods for sealing (packaging) an electronic device, a material comprising a thermosetting resin (e.g., epoxy resin) and inorganic filler particles dispersed into the resin is used as the packing material. Filler particle is used to decrease stress when the resin hardens, to increase the strength of the package and to improve the thermal conductivity. As a component of the filler particle, amorphous silica is used because of its excellent properties such as high electric insulation, heat resistance, low thermal expansion and affinity for thermosetting organic resins. (Hereinafter "silica" is referred to as "amorphous silica" or "amorphous silicon dioxide.") In addition, relatively pure silica can be prepared easily by synthetic methods or by purifying silica-containing material. Normally, silica particles used as filler will have a diameter of from about 1 .mu.m to about 100 .mu.m, depending upon the size of the package to be made.
The packing material can be manufactured by the following process steps:
(1) preparing silica particles by powdering and sieving high purity silica glass or sieving synthetic silica, such as that made from SiCl.sub.4 ; and
(2) dispersing the silica particles into a thermosetting resin, wherein the resin may comprise, for example, 30% by weight of the total weight of the dispersion.
A method for synthesizing silica by hydrolysis of alkoxysilane is also known.
Such a conventional packing material and a method for making it have the following disadvantages due to the fact that the silica particles are simply mixed and dispersed into the thermosetting resin:
(i) Since the thermal conductivity of the packing material is mostly determined by the filler particles, i.e., determined by the thermal conductivity of amorphous silica, to improve the thermal conductivity of the overall material is difficult.
(ii) As a result of (i), the conventional packing material cannot be sufficiently effective for more complex or larger electronic devices which generate more heat when used.
Accordingly, there is a need for an improved packing material which provides improved thermal conductivity.